JP6840637B2 - Method of forming fine dimples on the surface of hard and brittle materials - Google Patents

Description

The present invention relates to a method for forming minute dents (dimples) having an opening diameter on the order of microns on the surface of a hard brittle material such as ceramics.

The surface of the hard-brittle material in the present invention includes the entire surface made of the hard-brittle material, and not only the surface of the product made of the hard-brittle material but also the coating of the hard-brittle material formed on the surface of the product of various materials. For example, the surface of a ceramic coating is also included.

As an example of hard and brittle materials, ceramics are used as materials for various products and coating materials. Since they have high hardness and excellent heat resistance and wear resistance, they are products that come into contact with other members. , For example, it is used as a constituent material or coating material for sliding parts and mold surfaces.

By forming minute dents (dimples) on the surface of such sliding parts and molds and holding a lubricant, a mold release agent, etc. in the dimples, the frictional resistance of the sliding parts can be reduced or separated. Improvements in moldability are being made.

When the product to be formed of the dimples is made of metal, such dimples can be formed by plastically deforming the surface of the dimples. It has also been proposed to use the indentation generated by injecting and colliding the oil at a high speed as an oil reservoir for holding the lubricating oil (Patent Document 1).

However, when the sliding parts are made of ceramics or coated with ceramics, the ceramics have high hardness but are not easily deformed, and when a large force is applied, they are plastically deformed like metal. Since it is a hard and brittle material that breaks at once when it reaches the limit of strength, it is not possible to form dimples by plastic deformation like metal.

Therefore, the formation of dimples on the ceramics is adjusted so that the dimples are formed before firing the ceramics, or when the dimples are formed after the fact, they are formed by brittle fracture. It is formed by a method that does not depend on it.

As a method of forming dimples by adjusting before firing, a resin, a foaming agent, a whiskers, etc. are added to and mixed with a ceramic raw material, and the dimples are formed. ([0030] column of Patent Document 2), a method of molding a ceramic raw material before firing using a mold having a convex shape corresponding to dimples and then firing ([0031] of Patent Document 2). Column) etc.

In addition, as a method of forming dimples on ceramics after firing, the surface of a ceramic rolling element of a bearing or a constant velocity joint is irradiated with a single pulse laser having a pulse width shorter than that of a picosecond laser to make a minute amount. It has been proposed to form a simple dimple (Patent Document 3).

Japanese Unexamined Patent Publication No. 07-188738 Japanese Unexamined Patent Publication No. 08-128448 Japanese Unexamined Patent Publication No. 2016-156428

Among the dimple forming methods described above, the method of forming dimples by burning the added resin, foaming agent, etc. by adding and mixing a resin, a foaming agent, a whiskers, etc. to the ceramic raw material and then firing them is continuous. It is difficult to control the process to ensure uniform formation of independent dimples, and it is difficult to produce products of stable quality.

In addition, this method also requires adjustment of the type and amount of resin, foaming agent, etc. to be added for each type of ceramics used as the material for the manufactured product and for each type of manufactured product. Management is complicated.

On the other hand, in the method in which the ceramic raw material before firing is molded using a mold having a convex shape corresponding to dimples and then fired, all the products molded using this mold have the same position. It is possible to eliminate the variation in quality between the products in that dimples having the same shape can be formed.

However, the formation of dimples by this method is applied only to the products molded using the mold, and if dimples are to be formed on other products, it is appropriate for each product to be manufactured. It is necessary to prepare a mold in which convex portions to be dimples are formed in such an arrangement, which increases the manufacturing cost.

In particular, Patent Document 2 described above proposes forming a shape having corners such as a rectangle, a star shape, and a circular chain shape in addition to the hemispherical dimples. When moving, force is concentrated on this part, which causes destruction, and when a chip is generated, the debris generated by the chip damages the sliding surface and causes wear, which also causes absent wear.

Moreover, all of the above methods require advance preparation before firing in order to form dimples, and it is not possible to form dimples on the surface of the ceramic after firing.

Further, in any of the above-mentioned methods for forming dimples on ceramic products, dimples cannot be formed on ceramic coatings.

On the other hand, in the method described in Patent Document 3 in which minute dimples are formed by irradiating the surface of a ceramic rolling element with a single pulse laser, dimples can be formed ex post facto on the ceramic product after firing. It is also possible to produce products of uniform quality by forming dimples on each rolling element at the same size and at the same intervals.

However, when forming dimples by this method, it is necessary to irradiate the surface with a single pulse laser at regular intervals while rotating each rolling element in a predetermined direction to form dimples of the same size and at the same intervals. Therefore, a large initial investment is required because a complicated and expensive processing device that enables such a complicated operation is required.

Moreover, since it takes a long time to form dimples of the same size and at the same interval for each of the rolling elements, the cost of forming the dimples increases, and the price of the rolling elements in which the dimples are formed by this method is increased. It will be enhanced.

Furthermore, when dimples are formed by irradiation with a pulse laser, substances scattered from the surface of the material due to processing become fine particles called debris that adhere to the surface and become contaminated, and the debris slides between the friction surfaces. Since it causes abrasive wear in which the surface of the part is scraped off, it is necessary to remove this debris after forming the dimples.

In the above, the case of forming dimples for holding a lubricating material such as lubricating oil on the sliding surface of the sliding component has been described as an example, but the formation of such dimples is aimed at improving the releasability. It is not limited to the sliding surface of the sliding member, such as being provided to hold the release agent and air on the surface of the mold, and can be formed on the surface of various ceramic products and ceramic coatings. Therefore, there is a demand for a method capable of forming dimples on the surface of ceramics easily and at low cost.

The present invention has been made in response to the above-mentioned demands, and is a low-cost and processed product by a relatively simple method using an existing processing apparatus that can be introduced at a relatively low cost. It is an object of the present invention to provide a dimple forming method capable of forming dimples ex post facto on a hard brittle material typified by ceramics regardless of the shape and material of the material.

In order to achieve the above object, the method for forming fine dimples on the surface of a hard brittle material of the present invention is a method for forming a micro dimple on the surface of a hard brittle material such as ceramics or a product to be treated covered with a film made of a hard brittle material. Of the surface made of the hard brittle material of the product to be treated, such as the surface of the product, a substantially spherical jet particle having a median diameter d50 of 1 to 18 μm is formed from 0.01 MPa to the dimple-forming region, which is the region where the dimples are formed. by spraying with 0.7MPa injection pressure compressed gas, said dimple forming region hardness by recessing each collision portion of the injection granules of brittle material surface, by the plastic deformation regardless of the cutting Ride Inpuru (Claim 1).

Here, the "median diameter d50" is the cumulative mass diameter of 50%, that is, when the particle group is divided into two from a certain particle size, the integrated particle amount of the large particle group and the integrated particle group of the small side are integrated. It refers to a diameter at which the amount of particles is equal, and is synonymous with "particle diameter at a cumulative height of 50%" in JIS R 6001 (1987).

As an example, the dimples have an opening diameter of 1 to 20 μm and a depth of 0.01 to 1 μm (claim 2).

The dimples are preferably formed so that the total opening area of the dimples is 50% or more of the area of the dimple forming region (claim 3).

The hard and brittle material is preferably ceramics (Claim 4) or glass (Claim 5), and a sliding component made of ceramic is targeted for processing, and the sliding surface of the sliding component is the dimple-forming region. (Claim 6).

With the configuration of the present invention described above, the following remarkable effects could be obtained by the method of the present invention.

Dimples are applied to the surface of hard and brittle materials such as ceramics by an extremely simple method of injecting substantially spherical injection particles with a median diameter d50 of 1 to 18 μm together with a compressed gas with an injection pressure of 0.01 MPa to 0.7 MPa. I was able to form it.

Even with the formation of the dimples, the hard and brittle material did not break or crack, and the generation of cutting powder or the like could not be confirmed during the formation of the dimples. Furthermore, the ceramic product product after being treated by the method of the present invention ( As an example, the result of X-ray analysis of the surface of a cemented carbide containing WC as the main component shows that a significant increase in compressive residual stress (from -1000 MPa when untreated to -2200 MPa after treatment) was obtained. Therefore, it is considered that the dimple formation by the method of the present invention is not caused by brittle fracture but by plastic deformation of the surface of the hard brittle material.

Further, the dimple formation by the above method can be performed by a relatively short treatment using a known air-type blasting apparatus which is relatively inexpensive, and the cost required for dimple formation can be kept low. did it.

(A) of the mold of Example 1 is a surface micrograph, and (B) is a surface cross-sectional shape. (A) of the mold of the comparative example (untreated) is a surface micrograph, and (B) is a surface cross-sectional shape. Analysis image of von Mises stress by FEM (injection granules 10 μm). Analysis image of von Mises stress by FEM (injection granules 50 μm). The surface cross-sectional shape of the test piece (soda glass), (A) is an untreated state , and (B) is after the treatment according to the present invention .

Next, an embodiment of the present invention will be described below with reference to the accompanying drawings.

〔Processing object〕
The product to be formed of dimples by the method of the present invention (product to be treated) is a product having a hard brittle material or a surface coated with a film of a hard brittle material, the outermost surface of which is a hard brittle material. It is possible to target various products composed of.

The hard and brittle material includes not only ceramics but also single crystal silicon, etc., and the above-mentioned ceramics include mainly non-metals such as oxides, carbides, nitrides, borides, silices, fluorides, sulfides, and carbons. Including all inorganic solid materials composed of, for example, alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), silicon dioxide (SiO ₂ ), barium titanate (BaO ₃ Ti), yttrium oxide (Y ₂ O ₃ ), silicon carbide (SiC), tungsten carbide (WC), titanium carbide (TiC), silicon nitride (Si ₃ N _4), titanium nitride (TiN), titanium aluminum nitride (TiAlN), titanium boride (TiB _2), boride Glass mainly composed of zirconium (ZrB ₂ ), molybdenum _{silicate (MoSi 2} ), tungsten _{silicate (WSi 2} ), calcium fluoride (CaF ₂ ), diamond-like carbon (DLC), and silicon dioxide (SiO _{2) mentioned above.} (Soda glass, lead glass, borosilicate glass) and the like are all included in the ceramics in the present application.

Further, as long as it is a product made of the above-mentioned hard brittle material or a product coated with the hard brittle material, its use is not limited, and the method of the present invention can be applied to various products, and the surface of the product. Dimples can be formed on a part of the sliding member, and when applied to a sliding member used by sliding contact with other members such as bearings, shafts, and gears, sliding with other members among the sliding members. Only the moving part may be processed.

[Dimple formation method]
Of the surface of the product to be treated described above, a substantially spherical jet particle is injected together with the compressed gas onto the dimple forming region, which is a region where dimples are formed, and is subjected to a process of colliding with the above-mentioned region.

The injection granules, the injection device, and the injection conditions used when performing the above processing are shown below as an example.

(1) Injection Granules The "substantially spherical" in the substantially spherical injection granules used in the surface treatment method of the present invention does not have to be strictly "spheres" and is generally used as "shots". As long as the granular material has no shape, for example, even if it has an elliptical shape or a bale shape, it is included in the "substantially spherical injection granular material" used in the present invention.

As the material of the injection granules, either metal-based or ceramic-based materials can be used. As an example, the materials of the metal-based injection granules are steel, high-speed tool steel (high-speed steel), and stainless steel. , Chrome boron steel (FeCrB), etc., and as the material of the ceramic-based injection granules, alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), zircon (ZrSiO ₄ ), silicon carbide (SiC), etc. ), Hard glass, etc.

The particle size of the injection granules to be used can be in the range of 1 to 20 μm in median diameter (d50).

(2) Injection device As the injection device that injects the above-mentioned injection particles toward the surface of the product to be treated, a known blasting device that injects the abrasive material together with the compressed gas (air, argon, nitrogen, etc.) is used. can do.

Such a blasting device includes a suction type blasting device that injects an abrasive by utilizing the negative pressure generated by the injection of the compressed gas, and an abrasive that has fallen from the abrasive tank and is injected onto the compressed gas. A gravitational blasting device, a compressed gas is introduced into the tank into which the abrasive is charged, and the abrasive flow from the abrasive tank is merged with the compressed gas flow from the separately given compressed gas supply source and injected. Direct-pressure blasting devices and blower-type blasting devices that inject the above-mentioned direct-pressure compressed gas flow on the gas flow generated by the blower unit are commercially available. It can be used for injection of injection particles.

(3) Treatment conditions For the product to be treated described above, a substantially spherical injection granule having a median diameter d50 of 1 to 18 μm made of the above-mentioned materials is injected at 0.01 MPa or more and 0.7 MPa or less. Inject with a compressed gas of pressure.

As a result, dimples having an opening diameter of 1 to 20 μm and a depth of 0.01 to 1 μm can be formed on the surface of the hard brittle material.

The injection granules are injected so that the total opening area of the formed dimples is 50% or more of the area of the dimple forming region.

[Dimple formation test 1]
(1) Purpose of the test To confirm the change of state of the surface of the hard and brittle material due to the change of the injection conditions of the injected granules, and to confirm the improvement of slidability due to the formation of dimples.

(2) Test method The _{following is applied to the extruded mold for aluminum alloy made of zirconia (ZrO 2} ) (the surface is lap-polished to 0.1 μm or less with arithmetic average roughness (Ra)) as the product to be treated. The injection particles were injected under the conditions shown in Table 1.

The surface uneven shape of the untreated mold and the surface uneven shape of the mold after being treated under each of the above conditions were observed using a shape analysis laser microscope (“VK-X250” manufactured by KEYENCE CORPORATION).

Further, an aluminum alloy was extruded using an untreated mold and a mold treated under the conditions of Examples 1 to 3 above, and the state of aluminum adhesion to the mold surface was visually observed.

(3) Measurement results FIG. 1 shows the observation results by a laser microscope for shape analysis of the mold surface after forming dimples under the conditions of Example 1 described above, and FIG. 1 (A) shows the electrons obtained by photographing the mold surface. The microscope image and FIG. 1 (B) are cross-sectional shapes of the dimple formation position surface obtained from the analysis results.

Since substantially the same results were confirmed for the surface shape of the mold treated under the conditions of Examples 2 and 3, only the surface shape of the mold treated under the conditions of Example 1 was used as a typical example. The results of observation by the shape analysis laser microscope of the mold surface treated under the conditions of Examples 2 and 3 shown in FIG. 1 are not shown.

For comparison, FIG. 2 shows the observation results of the untreated mold surface with a shape analysis laser microscope. FIG. 2 (A) is an electron microscope image of the surface of the mold, and FIG. 2 (B) is a cross-sectional shape of the surface obtained from the analysis results.

Table 2 shows the results of observing the state of aluminum adhesion to the mold surface after extrusion molding using the dies of Examples 1 to 3 and the untreated (comparative example) dies.

From the comparison between FIGS. 1 and 2, the untreated mold surface (see FIG. 2), which was in a relatively flat state, was treated under the conditions of Example 1 and then the mold surface (see FIG. 1). ) Shows that dimples (hemispherical depressions) are formed.

Similarly, by observing using a shape analysis laser microscope, it was confirmed that dimples were similarly formed in the molds treated under the conditions of Examples 2 and 3.

No breakage or cracks could be confirmed on the surface of the mold after processing under any of the conditions of Examples 1 to 3, and no cutting powder could be confirmed during the processing. Furthermore, since a significant increase in the residual compressive stress was confirmed on the surface after treatment by the method of the present application, it is considered that the above-mentioned dimple formation was caused not by brittle fracture but by plastic deformation. Inferred.

Further, as shown in Table 2, it can be confirmed that in the mold in which the dimples are formed by the method of the present invention, the adhesion of aluminum is less likely to occur, and the dimples formed by the method of the present invention are the molding material. It has been confirmed that it contributes to the improvement of the slidability between the mold surface and the mold surface.

(4) Discussion The principle that dimples, which are considered to be due to plastic deformation, could be formed in zirconia, which is a hard and brittle material, without causing breakage or cracks by the method of the present invention is not always clear, but the method of the present invention does not necessarily clarify. It is considered that the formation of dimples by such plastic deformation was realized by using the injection granules having a median diameter (d50) of 1 to 18 μm.

That is, in order to cause plastic deformation in a hard and brittle material such as ceramics, it is considered that the permanent deformation energy per unit volume when a force is applied must be large, and in the case of the present invention, the jet particles are When a collision occurs, it is necessary to apply a large force (impact force) to a minute area.

Therefore, analysis by the Finite Element Method (FEM) when two types of steel jet particles (density 7.85) with a particle size of 10 μm and a particle size of 50 μm are made to collide with the workpiece (Finite Element Method: FEM) ( The results of simulating the Von Mises stress by (hereinafter referred to as "FEM analysis") are shown in FIGS. 3 (particle size 10 μm) and FIG. 4 (particle size 50 μm), respectively.

Here, FEM analysis is one of the numerical analysis methods, and when it is difficult to solve by an analytical method such as a complicated shape model, the region is divided into minute elements, a simple equation is set up for each element, and an interpolation function is used between the elements. This is a method of obtaining the solution of the entire region by approximating with, and here, "Femap with NX Nastran" (manufactured by NST Co., Ltd.) was used as the analysis software.

The "von Mises stress" is the equivalent stress based on the shear strain energy theory, which is expressed as a scalar value without direction, and is a stress field in which a load is applied in a complicated manner from multiple directions. The value projected onto the tensile or compressive stress of.

By referring to this von Mises stress, it becomes an index to judge whether or not this material yields, and when comparing with the yield stress, it is not necessary to look at the stress in the other direction, and it is judged by one von Mises stress. In view of the points to be obtained, this was used to simulate the stress generated by the collision of the injected particles.

From the simulation results, looking at the relationship between the particle size of the injected particles and the depth at which stress is applied, the smaller the particle size of the injected particles, the stronger the stress is applied to the very shallow layer on the surface, and the larger the particle size. It can be seen that the stress enters deeper layers, but the stress is smaller.

In the contour diagrams of FIGS. 3 and 4, the center of the crescent-shaped portion represents the portion where the stress is most intense.

The maximum stress, 8.752kgf / mm ² in the injection granules of 10 [mu] m, the injection granules of 50μm was 6.084kgf / mm ^2, the injection granules of 10 [mu] m, compared to the case of 50μm injection granules The maximum stress is 1.4 times.

Moreover, the depth at which the maximum stress is generated is 2.33 μm in the case of the injection granules having a particle size of 50 μm, whereas it is 0.40 μm in the case of the injection granules having a particle size of 10 μm, which is about 1/6. Therefore, the impact force per unit volume becomes dramatically the same as the particle size of the injected granules becomes smaller.

Therefore, in the method of the present invention using injection granules having a median diameter (d50) and a fine particle size of 1 to 18 μm, an impact force exceeding the yield point can be applied to the surface of the hard brittle material product. As a result, it is considered that dimples were formed by plastic deformation.

[Dimple formation test 2]
(1) Purpose of the test It is confirmed that dimples can be formed by the method of the present invention even for a hard brittle material other than zirconia, which was treated in the above-mentioned [Dimple formation test 1].

(2) Test method An untreated soda-glass test piece (length 10 mm × width 10 mm × thickness 2 mm) and a soda-glass test piece after injecting jet particles by the method of the present invention to form dimples, respectively. The surface shape of the glass was observed using a shape analysis laser microscope (“VK-X250” manufactured by KEYENCE CORPORATION).

The injection granules were injected onto the entire surface of the test piece under the injection conditions shown in Table 3 below.

(3) Measurement Results The surface shape (cross section) of the untreated test piece is shown in FIG. 5 (A), and the surface shape (cross section) of the test piece treated by the method of the present invention is shown in FIG. 5 (B).

The surface of the untreated test piece [FIG. 5 (A)] was flat without any noticeable unevenness, but in the state after treatment by the method of the present invention [FIG. 5 (B)], dimples were formed. I was able to confirm that.

Also, in the test on soda glass, it is not possible to confirm the occurrence of breakage or cracks in the test piece after treatment, and it is not possible to confirm the generation of cutting powder of soda glass due to collision with the jet particles. Furthermore, since compressive residual stress is applied, it is inferred that the dimples were obtained by plastic deformation.

(4) Discussion From the above results, it was confirmed that the method of the present invention can form dimples not only on zirconia but also on the surface of soda glass by plastic deformation.

From this, it can be reasonably inferred that the method of the present invention is not limited to the zirconia and soda glass treated in the examples, but can also be applied to the formation of dimples on other hard and brittle materials.

The method of the present invention described above can be applied to all applications requiring the formation of dimples on the surface of a hard brittle material.

As an example, to give an application example to a ceramic product or a ceramic-coated product, the dimples are formed on the sliding surface of the sliding member to hold the liquid / solid lubricant on the timples, and the dimples are used as air reservoirs. Friction resistance can be reduced by reducing the contact area.

Further, by forming the dimples on the surface of the mold, it is possible to maintain the release agent on the dimples and improve the releasability by reducing the contact area by using the dimples as an air reservoir.

In addition, by forming dimples, the surface of ceramics can be made a surface with excellent retention of various liquids (chemicals, perfumes, oils, oils, etc.), so that liquids such as ceramic water supply rollers used during printing can be used. Applicable to various ceramic products that require improved liquid retention, in addition to the above-mentioned treatments aimed at improving slidability, such as surface treatment of ceramic rollers used for applying oils and fats. Is.

Claims (6)

Of the surface made of the hard brittle material of the product to be treated, substantially spherical injection particles having a median diameter d50 of 1 to 18 μm are formed at 0.01 MPa to 0.7 MPa with respect to the dimple forming region, which is the region where dimples are formed. is injected with compressed gas injection pressure, the by recessing each collision portion of the injection granules of the hard brittle material surface dimple formation region to form a by Ride Inpuru plastic deformation regardless of the cutting that A method for forming fine dimples on the surface of a hard and brittle material. The method for forming fine dimples on the surface of a hard brittle material according to claim 1, wherein the dimples have an opening diameter of 1 to 20 μm and a depth of 0.01 to 1 μm. The method for forming fine dimples on the surface of a hard brittle material according to claim 1, wherein the total opening area of the dimples is formed so as to be 50% or more with respect to the area of the dimple forming region. The method for forming fine dimples on the surface of a hard brittle material according to any one of claims 1 to 3, wherein the hard brittle material is ceramics. The method for forming fine dimples on the surface of a hard brittle material according to any one of claims 1 to 3, wherein the hard brittle material is glass. The method for forming fine dimples on the surface of a hard brittle material according to claim 4, wherein the sliding component is the product to be treated and the sliding surface of the sliding component is the dimple forming region.